Air Handling Units (AHUs) are one of several components in cooling and heating systems. They are an important component as the AHU houses a number of components used in the system to provide forced air for climate control in a particular structure. AHU components typically include motors, heating/cooling coils, and blowers as well as the required interface connections to effect such climate control.
The AHU is an enclosed interconnected framed panel structure. The framed panel structures have insulated panels that are supported between framing members, also referred to as raceways, to define interconnected rectangular compartments. AHUs are typically large and bulky, the amount of floor space required to accommodate the AHU being commonly referred to as a “footprint.” Due to the layout of a particular structure, the AHU may be located in any number of locations, including rooftop installations, wherein the AHU is exposed to the rigors of environmental exposure, such as rain or snow.
Due to the bulky construction the AHUs, it is generally not possible to deliver the AHU fully assembled. Therefore, AHUs typically are constructed in modular sections which are brought together and assembled on-site. This imposed size restriction often results in the severing of otherwise continuous spans of the raceways, which severed ends of the raceways being referred to as “splits.” Such splits interrupt the structural integrity of the raceways and further complicate AHU on-site installation. To further complicate matters, raceways are typically constructed of non-metal materials having lower mechanical strength properties, generally rendering non-metal raceways nonusable for attaching lugs to provide a means for lifting the modular unit, much less the entire AHU once assembled. Non-metals, such as plastic or other polymers, may be selected instead of metal out of concerns for corrosion of metallic raceways and the higher thermal conductivity of metal. The higher thermal conductivity of typical metallic raceways may not only decrease the efficiency of the heating and cooling system, but may also result in the production of condensation in or adjacent the raceways, further promoting corrosion of the metallic raceways.
The insulated panels that are supported between raceway frames typically are required to include stiffening members to provide the necessary structural stiffness, especially when the insulated panel comprises the floor of the AHU compartment. These stiffening members add component cost as well as assembly cost to the AHU. Additionally, due to the increased stiffness requirements of the insulated panels when used as floors, different panel constructions may be required.
While the AHU construction may be considered bulky, typically its size is dictated by the component configuration selected and performance requirements associated with those components for efficient operation. In fact, an interior compartment containing a blower assembly and the associated driving means, typically a motor and drive belt arrangement, leaves little remaining space for installation or maintenance after subtracting the volume already occupied by insulated panels, support structure, wiring and other components. Despite such limited space, it is critical that the blower assembly and the driving means be properly aligned, and in the case of a belt drive, that a sufficient, but not excessive, amount of belt tension be provided. Failure to provide proper alignment and belt tension may both decrease the operating efficiency of the motor and blower assembly and cause premature failure of the belt, bearings or associated components, and may cause nuisance tripping of the motor overload switch due to overloading the motor. Additionally, movement, or slippage, between the belt and the driving means may generate noise due to inadequate belt tension.
In response to this concern, Japanese Publication No. 02225850A is directed to a pair of adjustable pneumatic dampers interposed between a blower and a motor for maintaining both a parallel alignment between the rotary shafts of the blower and the motor and constant belt tension. In response to changes in belt tension during the operation of the motor and blower, valves within the dampers regulate the amount of force exerted by one damper with respect to the other to provide the parallel alignment between the rotary shafts of the blower and the motor. However, the requirement for pneumatic dampers, a pneumatic source for adjusting the pneumatic dampers, valves, and the control system necessary to monitor and maintain both alignment and belt tension adds significant costs to the AHU construction. Further, periodic monitoring of the alignment as well as using a belt tension gauge which may be performed as part of routine maintenance, such as fan bearing lubrication, generally effectively addresses this issue.
In addition to alignment and belt tension issues with the blower assembly, since the compartment containing the blower assembly and motor is often mounted atop other AHU structure to reduce the footprint, vibration isolation is highly desirable. That is, by virtue of the operation of the motor and blower assembly, vibrations may be produced that could otherwise propagate to adjacent AHU structure and possibly to ductwork, generating noise or possibly causing damage to components subjected to these vibrations.
In response to this concern, U.S. Pat. No. 5,396,782 is directed to an integral suspension system for an air conditioning system adapted for mounting the air conditioning system to a support surface. Substantially enclosed spring support receptacles are formed at each end of Z rails for securing springs therein. A set of four retaining bolts is arranged within the spring support receptacles for contacting the outer periphery of the base coil of the spring when mounted within the receptacle to prevent lateral movement of the spring. The springs collectively support the Z rails which likewise support cross channels for mounting AHU components. However, this suspension system construction requires specially configured structural components that may add significantly to the cost of the AHU.
What is needed is an air handling unit construction provided with the following features: a single raceway construction having both low thermal conductivity and sufficient mechanical properties for use with lifting the AHU; a single insulated panel construction having a minimum number of components as well as sufficient structural stiffness for use as the floor in an AHU compartment; an insulated roof construction that prevents the collection of standing water on the top panel when subjected to environmental exposure; a motor belt tensioning/alignment arrangement that is easily adjusted and accessible in especially tight quarters; and a vibration isolation device having a minimum number of components with no specially machined structural parts to minimize costs associated with fabrication and installation.